Fish possess a skeletal structure that has a vertebral column or back bone from which spines extend upwardly (dorsal spines) and downwardly (ventral spines). No ventral spines are located in the region of the fish's belly cavity, however. Vertebrae extend over the top of the belly cavity for a short distance on either side of the mid-line, from which rib bones depend and curve downwardly to enclose the belly. Pin bones extend horizontally from the rib bones and terminate at or near the skin. For example, there are typically about forty pin bones in salmon.
The conventional method of filleting fish, by hand or machine, is to cut through the fish following the line of the bones from the dorsal to ventral fins and to pass over the rib bones, which severs the connections between the pin bones and the rib bones. In this method, a line of pin bones remains in the fillet.
There are two common methods used to remove the pin bones that remain in the fillet. In a first method, the pin bones are cut out of the fillet. For this method, filleting machines exist in the prior art that can produce bone-free fish fillets, but the yield is substantially lowered since the whole belly flap is cut off to ensure complete removal of the pin bones. The flesh of the belly flap can be recovered in a minced form after its passage through a bone separating device. However, since salmon and other fish are expensive, removal of the pin bones without extracting substantial quantities of meat is desired.
In a second method for removal of the remaining pin bones, the pin bones are pulled out of the fillet. In the oldest technique, the pin bones are pulled using a gripping tool, such as pliers. However, this option is time-consuming and labor-intensive, which results in higher cost to the consumer and potential injuries to the workers, such as, for example, carpal tunnel syndrome.
U.S. Pat. No. 4,771,511 to Weyand discloses a tool to simultaneously remove multiple pin bones, instead of individually pulling the pin bones out. The disclosed device includes a pair of opposed plates attached to forceps. The plates are configured to allow the device to remove more than one pin bone at a time. However, this technique still relies on manual labor and, thus, suffers from the disadvantages discussed above.
U.S. Pat. No. 4,945,607 to Akesson, et al. discloses a pair of jaws used in another prior art technique. Here, one of the jaws is fixedly positioned and the second jaw is pivoted relative to the first jaw by a pneumatically-operated cylinder between an opened position and a closed position. When the pin bone is positioned between the jaws in the opened position, the cylinder moves the second jaw to the closed position, which grasps the pin bone so that the pin bone may be pulled out of the fillet. This device, however, is bulky and difficult to align with the pin bones.
Still another prior art device is a rotatable cylinder having a plurality of holes for receiving fish bones. In use, when the operator moves the rotating cylinder across the surface of a fish fillet, pin bones are caught in the holes in the cylinder. To ensure that the bones are held to the hole and pulled from the fillet, a tongue or lip moves to grip the pin bone against the edge of the hole. After the pin bone is removed and as the cylinder spins away from the fillet, the tongue separates from the edge of the hole to release the pin bone. A vacuum suction device conveys the bone away from the cylinder and into a collecting receptacle. U.S. Pat. No. 5,525,101 to Soderlind discloses an embodiment of this design.
This rotatable cylinder design has drawbacks. One problem is that when the operator moves the cylinder across the fillet, it obscures the area where the bones are picked up. Consequently, the pin bones are easily flattened so that the cylinder does not catch the bones, hindering the operator from removing all the bones and requiring the operator to repeat the process. Another potential problem is that the operator pressing the rotating cylinder against the fillet may potentially remove meat from the fillet and create a less appealing appearance. Additionally, the removed pin bones may become stuck in the cylinder holes used to remove the pin bones, which may eventually require an interruption in operation to clean the cylinder. In conjunction, thoroughly cleaning the device can be time-consuming and cumbersome. Cost is another drawback of the rotating cylinder design.
Another device, as described in U.S. Pat. No. 6,123,614 to Kozycki, uses a plurality of spring-tempered sheet metal disks that are assembled to form a stack of disks aligned so that the peripheries form at least one “pinch-point,” at which the periphery of two disks contact each other, to grip a pin bone. In operation, the stack of the disks is rotated and moved over the fillet and the pin bone is disposed between two adjacent rotating disks. As the gap between the disks closes to the pinch-point, the pin bone becomes wedged and is subsequently plucked out of the fillet as the wedged pin bone is pulled by the rotating disks. One problem with this design is that the pin bones may get lodged in the gaps of the disks and have to be manually removed.
Therefore, a need exists in the art for a relatively inexpensive device to remove pin bones from fish. It is desired that the device can be used in an automated process, instead of having an operator who removes the bones by manually maneuvering a machine or remove pin bones. Still another need in the art is for a device that reliably extracts the pin bones without removing a significant amount of meat from the fillet, creating an unattractive surface appearance, or otherwise damaging the fillet.